Every rider knows what you mean by “aids”. Actually, it is a crazy word, because you do not “aid” a horse. At least it shouldn’t be. Indeed, I sometimes see people trying to guide a horse through an exercise as if in a straightjacket between legs and hands, but that usually does not improve the situation. A horse can move fine by itself and everything we do only hinders that. The more you back off, the better. “Directions” is a better term. “Signals” could also be used. The bottom line is that you indicate something to your horse in a way that he understands what you want from him.
I have had the pleasure of interviewing Anky van Grunsven several times for my work. In the horse world you don’t have to explain to anyone who Anky is and that in itself is a phenomenal achievement. A conversation with her is always worthwhile, because she has a clear opinion and does not hide it. I once had a talk with her about aids and I have to conclude that I completely agree with her. Anky emphasized the importance of the unambiguous aids. Her opinion on this is endorsed by behavioral experts.
What exactly do we mean by unambiguous aids? That you have one clue for one response and that this does not conflict with any other clue. Let’s use as an example that you are doing a downward transition, but you want to keep your horse on his hind legs. So you close your hand for the “whoa”, but at the same time you give leg for the “go”. You brake and you accelerate at the same time. How should he figure out what you want from him?
Another one is: suppose you make a transition from trot to walk or from canter to trot. What do you do? More pressure on both reins? Then what do you do if you want your horse more round in the outline? Also more pressure on both reins? How does he know if you want more roundness or a transition?
Aids make sense
You can teach a horse almost anything. The aids we use have been developed over the centuries, because they made the most sense that way, especially for us. You can also teach a horse to canter by pulling his ear, but that is a rather difficult movement from the saddle. Due to the shape of our body and that of a horse, it is more natural to do something with your legs if you want to go forward. However, if you watch a cowboy movie you can see that a “Yee-haw” movement with flapping reins also has an effect. But that only looks good if you have fringes on your trousers and a Stetson on your head. We want it subtle and invisible in dressage, so your legs are the most logical instruments.
If you read it in a book it seems easy. Touching your horse briefly with both legs means forward and putting more pressure on both reins is “whoa”. You are also doing something with your seat, but what often remains somewhat puzzling. Sitting deep, lifting your ribcage, torso stability – those kind of vague terms.
If you look at the muscling of a horse, rein aids provide an effect that slows down the movement. Leg aids activate muscles that provide movement. A horse can do nothing with both aids at the same time, because the reactions cancel each other out. No matter how well riders try, conflicting aids are often given unconsciously at the same time. The horse reacts most to the “whoa”, because rein pressure comes through stronger. So, if you inadvertently give both at the same time, you teach a horse to ignore the leg aids. While the horse usually gets the blame. Many riders have installed a kind of hand brake themselves this way.